The present invention relates to a process to remove certain metals from crude oil. In particular, the metal is calcium.
Calcium present in crudes can lead to fouling of heaters and heat exchangers and poison catalysts used in crude processing. Therefore, Ca-rich crudes are less valuable than crudes with low Ca. A process for Ca removal enables the increase of the value of such crudes. This invention is particularly valuable when a Ca-rich crude is processed in a corrosion-resistant environment, where the increase in acidity accompanying the process of the present invention is not a drawback.
Some patent and published literature exists, dealing with metals removal from petroleum. One approach did not use carbon dioxide, instead contacting the petroleum with aqueous solutions of acids to effect metals removal as follows: Reynolds (U.S. Pat. No. 4,778,591) described a process for removing metals from petroleum using aqueous carbonic acids. In U.S. Pat. No. 4,853,109 Reynolds used aqueous dibasic carboxylic acids to remove metals from petroleum. Kramer et al. (U.S. Pat. No. 4,988,433) taught the removal of metals from petroleum using an aqueous monobasic carboxylic acid or its salt. In the other approach, Eckerman et al. (Chem. Eng. Technol. (1990), 13(4), 258-64) and Funk (Am. Chem. Soc. Div. Fuel Chem., (1985) 30(3), 148, 148a, 149, 149a, 150-3) reported on the use of supercritical CO.sub.2 fluid to deasphaltene heavy oils accompanied by some removal of only porphyrin metals (Ni, V) associated with the asphaltenes. This form of CO.sub.2 has different properties and different separation selectivity from the present invention.